function Food(el) {
    this.el = el
    this.len = 20
    this.foodObj = null
    this.foodX = 0
    this.foodY = 0
}
Food.prototype.create = function () {
    let divObj = document.createElement('div')
    divObj.style.width = this.len + 'px'
    divObj.style.height = this.len + 'px'
    divObj.style.background = 'pink'
    divObj.style.position = 'absolute'
    this.foodObj = divObj

    this.el.appendChild(divObj)
    this.move()
}

Food.prototype.move = function () {
    let foodxMaxNum = this.el.clientWidth / this.len - 1
    let foodYMaxNum = this.el.clientHeight / this.len - 1
    this.foodX = Math.floor(Math.random() * (foodxMaxNum - 0 + 1) + 0) * this.len
    this.foodY = Math.floor(Math.random() * (foodYMaxNum - 0 + 1) + 0) * this.len

    this.foodObj.style.left = this.foodX + 'px'
    this.foodObj.style.top = this.foodY + 'px'
}